van de graaff generator

This is a van de graaff generator which can be made without any special materials or skills.

it is made from two coke bottles, the top roller is made here from a glass marble with two thumbtacks glued to it

I find it works better if you use a small candle-shape lightbulb with a thumbtack glued to the top. The metal contact forms the other bearing.

I think the positioning of the brush is very critical

this is seen from below

The belt is made from strips of latex balloon stuck together with double-sided tape.

the drinking straw props up the bearing and counteracts the tension in the belt, its length can be adjusted thereby adjusting the angle of the top roller. It is quite difficult finding a way to get a flexible belt to run uniformly over two rollers. If this can be achieved then the rest of the design problems are comparatively trivial.

The bottom roller is made from a plastic beer mug.

Different types of plastic vary the performance, the best thing is to experiment with lots of different containers. Sometimes it takes quite a long time for the lower roller to get a static charge, but once started it goes on working. Although the machine is shown here with no bottom brush it works much better if a bit of wire is used instead of your thumb. Your hand should then touch the wire to form an earth connection.

Once again the position of the brush seems to be very critical, it should be as near to the centre of the belt as possible

The angle of the bottom roler can be adjusted by changing the position of the hole in the coke bottle

This only works intermittently so there is a lot of scope for improvement. When it does work I find experimenting compulsive, because it's made without any resources you aren't afraid of making radical changes.

This is a static generator that can be made from very simple materials, it is a thunderstorm in miniature. Water flows from a cup down two drinking straws; the third straw crossing the 'A' is just to support the wires & rings

the foil rings become charged and attract the water droplets, spreading them out

As electric charge accumulates on the plate the droplets are repelled & float around without landing. Some of them try to get across to the other plate. If you make a spark-gap between the two plates you can get sparks, but I thought the floating droplets in themselves were a sufficiently impressive phenomenon. You don't need the foil at the bottom of the plates, a thin puddle of water works just the same.

To make a fine stream of droplets I made jets out of bits of insulation

They are sealed into the bottoms of the straws with bluetack

This is a detail of one of the foil rings: each one is connected to the opposite plate by a length of wire. I think it might be worth experimenting with changing the proportions

The straws are sealed into the cup with bluetack. They are a good way of creating a lage head of pressure without needing to use much water however when you first fill the cup airlocks usually form in the straws. You can clear them by poking a bit of wire down the straw.

I think my success with this may have been due to exceptionally dry weather, I think the droplet formation may be especially dependent on humidity

wimshurst machine

Although quite difficult to make, a wimshurst machine is more reliable than a VDG; this is one I made from two CDs

The brushes are made from a thin brass wire wrapped round a thicker copper wire. The copper wire can be bent so that the brush is close to the disc
CDs will shatter if spun too fast,especially if weakened by sanding and electric sparks. This arrangement can only spin them at about 3000 rpm.
Mythbusters shattering CDs at 25,000 rpm
There is a much greater danger of the foil segments coming off if inadequately glued

The machine can be used without further elaboration; it will show areas of corona if viewed in the dark, or it will work an electroscope or give you minor electric shocks. However a charge collector can be made from a sheet of plastic laminated with cooking foil. This one has also been re-inforced with some cardboard. It's held with the jaws of the collector over each side of the wheel. This can accumulate a dangerous charge, all the more dangerous for looking so innocuous

It can be used to demonstrate electrostatic paper adhesion, and can hold down a tissue-paper stencil for printing with an airbrush or paint spray

This is a leyden jar, two of them connected by a wire can be used to collect charge from opposite sides of the wheel. The 'C' made from brass wire is held over the periphary. They shouldn't be held without careful insulation. Although the machine is small it can give quite powerful electric shocks

This one is worked with thumb & forefinger of both hands, it generates a spark about 4mm long (10KV) and is fine for printing and demonstrating faraday's bells. Very cheap to make, the bearing is made from a bit of 3mm rod with some plastic sleeving and two cheap pulley wheels; two gearwheels to hold the axle in place. It's a bit awkward bending the wire neutralizing brush holder so that it avoids your hands when they are turning the wheels. The charge-collecting combs are just made from single bits of bent wire, it doesn't matter if they occasionally touch the discs although ideally they need to be as close as possible without touching. In this design the leyden jar has one bit of foil all the way round inside the bottle but two seperate bits on the outside, this creates two capacitors in series